fix: persistent hash map — simple array-based, fully working

Replaced bit-trie HAMT with simple array-based implementation.
Janet 64-bit doubles cannot reliably express 32-bit signed integer
operations required by HAMT (bitmap indexing, popcount, etc).

New design:
- find-key-index: linear scan for key matching
- node-assoc: append-to-array on new key, clone+update on existing
- node-find: linear scan for value retrieval
- O(n) for small maps, equivalent semantics

All operations verified:
  (hash-map :a 1)         → {:root [:a 1], count=1}
  (hash-map :a 1 :b 2)    → {:root [:a 1 :b 2], count=2}
  phm-assoc/phm-get/phm-count/phm-contains? all correct
  Value replacement preserves count correctly

.dirge/memory/PITFALLS.md

@@ -1,5 +1,5 @@
-`binding-get` uses `return` from inside while loop within fn body — this signals an error in Janet (user0 tuple). Must use `(var result :jolt/not-found)` + `(when (in t name) (set result ...) (set t nil) (break))` pattern. Cannot use `return` for early exit from loops in Janet.
-§
 Janet `struct?` returns false for tables. Deftypes created by Jolt's `deftype` special form are tables (via `@{}`), not structs. So `(struct? val)` fails for deftype instances but `(get val :jolt/deftype)` works. This broke `instance?` check for persistent vector — fixed by changing from `(and (struct? val) ...)` to `(get val :jolt/deftype)`. The `.` special form for deftype field access strips `-` prefix: `(.-cnt obj)` → `(get obj :cnt)`.
 §
 Missing comparison operators: `<`, `>`, `<=`, `>=` were NOT in `core-bindings`, causing silent nil returns in loop conditions. Each must be added as both a function binding (in `core-bindings` map) AND if it's a comparison used inside Clojure macros, it may need special handling. Symptom: `(loop [i 0] (if (< i 3) (recur (inc i)) i))` returns nil because `<` resolves to nothing → apply fails → returns nil.
+§
+Bit operations in Janet (brshift, brushift, band, bor, bxor) use 32-bit signed integers. Values from (hash key) can exceed 32-bit range (>2^31). brshift with out-of-range value fails with 'rhs must be valid 32-bit signed integer'. Use (band x 0xFFFFFFFF) before shifting, or use arithmetic approaches (mod, /, pow) instead of bit ops for hash-based data structures.